Surgical Anatomy of Supratentorial Midline Lesions

from 0 to 7 (average, 1.1) per hemisphere, and their diameters ranged between 0.2 and 0.5 mm (average, 0.25)(Fig. 11 and Table 2).
Posterior pericallosal artery
The posterior pericallosal artery (also known as the splenial artery) contributed to the blood supply of the corpus callosum, in particular the
splenial portion, in all hemispheres. It arose from the main trunk of the parieto-occipital artery or its precuneal branch (52%), the P3 segment of
the PCA (32%), the calcarine artery (7%), the temporo-occipital artery (7%), or the P2 segment of the PCA (2%). Three anatomic variations of
the posterior pericallosal artery were identified: 1) proximal type (the origin of the artery was located a few millimeters inferior to the splenium
and followed an S-shaped course toward the splenium [80%]); 2) distal type (the artery generally arose from a precuneal branch of the
parieto-occipital artery and was located posterior to the splenium [10%]); and 3) double type (both proximal and distal arterial patterns were
observed, and they anastomosed with each other within the callosal sulcus [10%]).
In all three variations, the posterior pericallosal artery divided into two main branches when it reached the splenium. The superior branch
formed the main trunk and coursed within the callosal sulcus with a characteristic corkscrew-like tortuousity; it then anastomosed with the
posterior extension of the A5 segment in 65% of the hemispheres. When the long callosal and/or the median callosal arteries were present, they
were also occasionally involved with this anastomosis. In 35% of the hemispheres, the A5 segment coursed in the cingulate sulcus. In this
instance, the median callosal and/or the long callosal arteries were dominant and anastomosed exclusively with the posterior pericallosal artery.
All variations of these complex anastomoses formed the dense portion of the pericallosal pial plexus within the callosal sulcus in the splenial
region. In 77.5% of the hemispheres, the inferior branch ran anteriorly and then gave rise to branches supplying the tail of the hippocampus,
and/or the pulvinar of the thalamus, and/or the tela choroidea of the third ventricle. In the latter situation, it usually anastomosed with the medial
posterior choroidal artery and occasionally reached as far as the foramen of Monro. In the remaining 22.5% of the hemispheres, the inferior
branch was thin and short and supplied the fasciolar gyrus and the crus of the fornix. The posterior pericallosal artery ranged in number between
1 and 2(average, 1.1) per hemisphere, and its diameter ranged between 0.4 and 1.0 mm(average, 0.7 mm) (Figs. 1, 7, A-C, 8, A and B, 9-11).
FIGURE 7. Anatomic variations of the posterior pericallosal artery. A, proximal type. In 80% of the hemispheres, the posterior pericallosal
artery (arrowhead) arises from the PCA or one of its main branches, inferior to the splenium( S). B, distal type. In an additional 10% of
hemispheres, the posterior pericallosal artery( arrowhead) generally arises from a precuneal branch of the parieto-occipital artery, posterior to
the splenium.C, double type. In the remaining 10% of the hemispheres, both proximal and distal type arteries are present( arrowheads). In all
instances, the posterior pericallosal artery courses toward the splenium, where it divides into two main branches, superior and inferior .